In the manufacture of large rotating machines, epoxy resins have long been used as impregnants for insulation which relies upon mica, in the form of paper, flakes or large splittings as the dielectric. In this art, epoxy acid anhydride systems are generally catalyzed with materials such as dicumyl peroxide and tetiary butylperbenzoate, as in U.S. Pat. No. 3,647,611, or with quaternary organic phosphonium compounds, as in U.S. Pat. No. 3,759,866. These catalyzed, epoxy; acid anhydride impregnants are then vacuum impregnated into prewound mica tape insulated coils.
Vacuum impregnation, however, is costly and time consuming, but has generally been considered necessary to get a void free insulating tape. Groff, in U.S. Pat. No. 3,660,220, used a mica-glass cloth tape, pre-impregnated with an epoxy resin-oil modified acid anhydride solution, as a pre-preg electrical insulation for motors. These solutions were catalyzed with stannous octoate, tertiary amines or boron trifluoride complexes. These catalysts, however, provide poor high temperature electrical dissipation (power) factor values, i.e., about 25% at 155.degree. C. Also, these mica tapes would not retain their initial flexibility after storage.
While the epoxy pre-preg tape concept is an improvement in the art, it presents a host of problems with respect to tape tensile strength, void-free resin impregnation, maintenance of flexibility after solvent flash off, and retention of tape flexibility after long periods of storage i.e., over 6 months. What is needed, is a new type of resin-mica, catalyzed insulation tape, for high voltage motors and large rotating machines, that will retain flexibility after long term storage, and will provide improved power factor values.